Dr. Alice Frei, who has been monitoring the 30-pound cat's progress at the Southside Place Animal Hospital, today announced Tiny's "aggressive tumor" on his Facebook fan page, "Tiny Tim at Spah."

"Tiny Tim has cancer," Frei wrote. "There is no radiation or chemotherapy for such an aggressive tumor."

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Frei said Tiny was rushed to Texas A&M University School of Veterinary Medicine for treatment on Wednesday after SPAH staff noticed his elbow was swollen and pathology results showed cancer. A&M veterinarians confirmed the pathologist's findings, and "said the cancer was so rapidly growing that they could not define the cell of origin," Frei wrote.

Tiny is scheduled to have a CAT scan on Friday to see how far the tumor has spread. The SPAH staff will then assess a treatment plan, but options for the beloved cat seemed dire.

"If Tiny Tim's CAT scan does not show [the] tumor has invaded his chest, we have decided that the only course of treatment is to have the leg amputated," Frei wrote. "If the tumor has spread to his chest his treatment options are basically zero."

The staff is now waiting to see if Tiny will need surgery, but even that will be a difficult decision.

"Surgery for Tiny Tim is a huge risk because of his size, and if he makes it through the surgery he has a long road back," Frei wrote. "It will be rough. With it he may die. Without it he will die."

Tiny, who's about 9 years old, weighed in at a hefty 35.2 pounds when he arrived at the animal hospital around Christmas 2011, but testing showed that Tiny was otherwise healthy. When a search for his owner proved unsuccessful, the hospital took him in as a permanent resident -- provided he'd lose weight.

By New Year's, the "super sweet cat" had been placed on a strict diet for the year.

"He has been on a very, very regimented diet -- measured meal plans, the whole works, and he is at 28.6 pounds," SPAH manager Debbie Green told ABCNews.com in a recent interview. "He weighs in twice a week, and he gets meals measured in little bags throughout the whole week, so we know exactly what he's eating."

Tiny is fed a precise 307 calories per day, and his team of doctors would be "really, really excited if he got closer to 20 pounds," Green said.

Earlier this year, Tiny seemed to plateau at 30 pounds. The cat, somewhat ironically, lives in a food pantry in the animal hospital because he is too big for the normal cat cages at Southside. A staff member figured out Tiny had clawed a small hole into a bag of food and had been having midnight snacks.

Tiny's doctors make sure Tiny exercises by making him work for his bed and board. He is carried to the front of the clinic at least three times a day, and he has to walk the 50 feet back to his room for meals.

"He doesn't voluntarily walk around the office," Green said. "He used to move 10 steps and then sit down. Now he can get from the front to the back, which is about 50 feet, without much trouble at all."

Tiny's cancer hasn't been the only health concern for the SPAH staff. He is also at risk for feline diabetes or thyroid problems in the future because of his weight, Green said. They believe arthritis could become a problem for him too.

Regardless, the popular feline is usually pretty quiet and prefers the peace of his pantry to the business of the hospital's waiting room, but he enjoys the attention and brushing he receives from friends and fans who often stop by to visit him.

Tonight, he remained at the A&M veterinary hospital, where "he is doing fine, has the entire cat ward to himself and is getting lots of attention," according to his Facebook fan page.